hi, i had highlights too, not platinum blonde, more of an ash blonde done with feria's diamond blonde collection. the glaze (john frieda's stuff anyways) just makes them like darker color. in my case it toned down the highlights to like a light ash brown/dirty blonde color which then helped me to bring all of my hair color to the same level (then i died it with natural match by loreal) i highly doubt they'll turn green, but if anything bad happens, use dishwashing liquid and it will remove unwanted residue on your hair

Thanks so much for the advice! I was planning on buying some Glaze today. I hope it turns my highlights a bit darker without adding any funky coloring to it. But even if it does, I have a hair appointment scheduled for next week.

Why brunette is betterMatthew Waldron, a colourist and hairstylist at Mood by Pure in Montreal, says brunette is the perfect match for gals who can’t deal with high-maintenance locks. “Brown hair only needs to be touched up every 2–3 months, so it’s cheaper, too.” And the reasons to go brown don’t stop there. Waldron adds:
• Brown hair makes skin look energized and eyes and teeth appear whiter.
• If you’re a thin- or fine-haired gal, brown beats bad-hair days by providing extra body and shine, thanks to hair-enriching pigments.
• Dark hair best hides split ends and damage caused by blow-dryers and flatirons.
• Add mocha to mousy and watch your hair get added oomph and vibrancy.
• Brunette hair reflects more light than blond or red hair, so you’re guaranteed to shine.
• Almost anyone can be a brunette (consult your colourist for his pro opinion), but note that no skin tone is better suited to chocolaty strands than olive.
from flare.com